An assistant professor at the University of Tokyo, Kaneko is the mild-mannered side of "Mr. 47", author of Winny, an encrypted successor to the WinMX p2p file sharing program. It is widely used in Japan with perhaps as many as a quarter million users, much to the consternation of authorities. Kaneko was arrested 10 May 2004 for "conspiracy to commit copyright violations" likely because of his advocacy of disrupting the current copyright regime.